Oxygen

In nature, oxygen is found in the Earth's crust, 46.6 % (w/w), and Earth's atmosphere, 20.95 % (v/v) [4]. The isotopes found in nature are ¹⁶O (99.759 %, stable), ¹⁷O (0.037 %, stable) and ¹⁸O (0.204 %, stable) [4].